<div id="app">
  <div class="color" :style="{backgroundColor: `rgb(${R},${G},${B})`}"></div>
  <div>
    <input type="range" v-model="R" min="0" max="255" /> R  {{R}} <br>
    <input type="range" v-model="G" min="0" max="255" /> G  {{G}} <br>
    <input type="range" v-model="B" min="0" max="255" /> B  {{B}} <br>
  </div>
</div>
<script src="https://unpkg.com/vue@next"></script>
<script>
  Vue.createApp({
    data() {
      return { R: 0, G: 0, B: 0 }
    }
  }).mount('#app')
</script>
<style>
.color {
  width: 40px;
  height: 40px;
}
</style>